Ball and track grinding mill with drive means arranged such that drive torque reaction will maintain pressures between the balls and tracks



May 21, 1957 L. SZEGO A 2,792,994

BALL AND TRACK GRINDING MILL WITH DRIVE MEANS ARRANGED SUCH THAT DRIVE TORQUE REACTION WILL MAINTAIN PRESSURES BETWEEN THE BALLS AND TRACKS Filed May 11 1954 2 Sheets-Sheet 1 /VVE/VTOR 42152. 0 52560 BY e ATTORNEYS May 21, 1957 2930 I 2,792,994 I BALL AND TRACK GRINDING MILL WITH DRIVE MEANS ARRANGED SUCH THAT DRIVE TORQUE REACTION WILL MAINTAIN PRESSURES BETWEEN THE BALLS AND TRACKS 2 Sheets-Sheet 2 Filed May 11, 1954 IN V! N TOR LAsZLo 52560 A TTOR/VE Y6 United States P n BALL AND TRACK GRINDING MILL WITH DRIVE MEANS ARRANGED SUCH THAT DRIVE TQRQUE REACTION WILL MAINTAIN PRES- SURES BETWEEN THE BALLS AND TRACKS Laszlo Szego, Greenwich, London, Engiand Application May 11, 1954, Serial No. 429,056 Claims priority, application Great Britain May 13, 1953 7 Claims. (Cl. 241 -105 This invention relates to grinding machines for reducing materials to particles of very small size, either in the dry state, or in the presence of liquid to form an emul-.

comprises a fixed track ring provided on its radially inner side with a track of arcuate cross section, a rotatable shaft extending through the fixed track ring and carrying a rotatable track ring, a set of balls arranged between the fixed track ring and the rotatable track ring, and driving means between the shaft and the rotatable track ring so arranged that the torque reaction during rotation of the shaft tends to urge the rotatable ring axially along the shaft, the track on the rotatable track ring being so shaped that the axial thrust on the said ring urges the balls outwardly against the fixed track ring.

In a preferred form of grinding machine according to the invention two axially spaced fixed track rings are provided, and the rotatable shaft carries two rotatable track rings, two sets of balls being provided, each between one fixed track ring and one rotatable track ring, the driving means being so arranged that the two rotatable track rings are urged axially in opposed directions.

The driving means may comprise a screw or equivalent mechanism, and in a preferred embodiment of the invention consists of a plurality of balls engaging" helical grooves in the rotatable shaft and in the rotatable track rings.

The invention is hereinafter described with reference to the accompanying drawings, in which:

Figure 1 is a vertical section through one form of grind ing machine according to the invention having two grinding stages;

Figure 2 is a sectional plan view of the grinding machine shown in Figure 1 taken on the line 2-2 of Figure 1; and

Figure 3 is a similar section through a mill having a larger number of stages.

Referring to Figure 1, the grinding machine comprises a cylindrical casing 19 mounted between upper and lower end caps 11 and 12, between which are clamped two fixed track rings 13 and 14 spaced apart bya spacing ring 15. Arcuate track grooves 16 are formed in the inner surfaces of the track rings 13 and 14. A driving shaft 17 passing upwardly through a central opening in the lower end cap 12 has keyed to it a driving sleeve 18 from the longitudinal centre of which extend two helical grooves 19 and 21 of-opposite hand. Two rotatabletrack rings 22 and 23 surround the sleeve 18, one on each side of the longitudinal centre of the said sleeve, the track ring 22 being formed internally with a helical groove 24 of the same hand as the groove 19, and the track ring 23 being formed internally with a helical groove 25 of the same hand as 2,792,994 in Patented May 21, 1957 the groove 21. A row of driving balls 26 is engaged in both grooves 24 and 19, and a similar row of driving balls 27 is engaged with both grooves 25 and 21, each row of driving balls being located by a cage 28. The outer side of each track ring 22 and 23 is formed with a track 29 having a curved profile in cross-section such that the radius of the track 29 increases toward the side of the track ring nearer to the longitudinal centre of the sleeve 13. Grinding balls 31 form two rows, one between the track rings 13 and 22 and the other between the track rings 14 and 23.

The driving shaft 17 is rotated in such a. direction that drag on the track rings 22 and 23 tends to produce relative turning movement of the shaft 17 and the track rings 22, 23 in a direction such that the said rings 22 and 23 are urged axially apart, thus, due to the shape of the tracks 29, thrusting the grinding balls 31 outwardly against the track rings 13 and 14, and so increasing the pressure between the balls 31 and the track rings.

Material to be ground is fed into the machine through a hopper 32, and is distributed by a cone 33 rotating with the sleeve 18, the hopper 32 leading into a feed tube 34 terminating just above the surface of the cone 33. The position of the feed tube 34 is adjustable to vary the rate at which material is fed to the machine, the feed tube 36 having screw-threaded engagement at 35 with the end cap 11, and being locked in position by a locking ring 36.

A tapering annular air passage 37 is formed in the end cap 11, the said passage opening into the interior of the machine through an annular slot 33. Air blown into the large end of the passage 37 provides a whirling current of air entering the grinding chamber through the slot 38, the tapered form of the passage 37 causing the air to be substantially evenly distributed around the circumference ofthe slot.

The end cap 12 is formed with a similar tapered annular air passage 39, opening into the grinding chamber through a slot 41. i

The rotating cone 33 throws the material outwardly into the pass between the grinding balls 31 and the track groove 16 in the track ring 13, the material being crushed by the rolling action of the balls on the said track ring. The air current through the slot 38 facilitates the even distribution of the material. The rotation of the grinding balls throws the material outwardly, as it leaves the first pass, into the pass between the balls 31 and the track groove 16 in the track ring 14, where further grinding takes place, the material leaving the second pass being guided by an inclined skirt 42 rotating with the sleeve 18 into the slot 41 and so into the passage 39, from which it is removed by suction applied to the larger end of that passage, or by the current of air blown into the upper end of the machine.

It will be understood that the presence of material to be ground between the balls 31 and the track grooves 16 creates a resistance to rotation of the track rings 22 and 23 which depends on the quantity of material present, and the pressure of the balls 31 on the track grooves 16 will thus vary with the quantity of material fed to the machine. When there is no material passing through the machine, there is very little resistance to rotation of the track rings 22 and 23. As no substantial pressure is exerted between the grinding surfaces except when there is material to be ground between them, very little wear of the said surfaces takes place, the material to be ground acting, like a lubricant, to prevent direct engagement of the surfaces. As the drive is applied to the inner track rings 22 and 23, and the crushing or grinding action is effected between the balls 31 and the outer track rings 13 and 14, the balls 31 rotate more slowly than the driving shaft 17, thus reducing the power necessary to drive the machine.

The multi-stage grinding machine shown in Figure 3 operates on the same principle as that shown in Figure 1. The machine comprises a cylindrical body 44 closed at its upper and lower ends respectively by end caps 45 and 46 in which are formed'inlet and outlet passages 47 and 48 respectively, and a driving shaft 4-9 extending upwardly through a packing gland 51 in the lower end cap 46. Mounted in the body 44, and held against rotation therein by a key 52, are a plurality of track rings 53, the end track rings 53 engaging shoulders 54 on the end caps. Alternate spaces between the track rings 53 are occupied by compressible spacing rings 55, for example of indiarubber, the intermediate spaces being occupied by noncompressible spacing rings 56, for example of steel.

The lower part of the driving shaft 49 has keyed to it, by a key 57, three double track rings The said double track rings 53 may be integral units, the upper two such track rings being shown in this form, or may each consist of two separate track rings 58a, the lowest ring being shown in this form. Each double track ring co-operates with rows of grinding balls 59 engaging two adjacent track rings 53 separated by a compressible spacing ring 55, the double track rings being free for limited axial movement on the driving shaft, and the gaps between them being covered by deflector rings 61. The upper end of the driving shaft 49 is reduced in diameter and has keyed to it by a key 62 a driving sleeve 63 formed externally with divergent helical grooves 64 and 65, and surrounding the sleeve 63 are two single internal track rings 66 formed internally with helical grooves 67 and 63 of opposite hand, driving balls 69 being located in the mating grooves 64 and 67 and in the mating grooves 65 and 65. Grinding balls 59 are disposed between the inner track rings 66 and the upper two outer track rings 53.

When the machine is in operation, resistance to rolling of the grinding balls 59 on the upper two track rings 53, due to the presence of material to be ground, causes the inner track rings 66 to move axially away from one another, thus pressing the balls 59 engaging those track rings more firmly against the outer track rings 53, and tending to move the track ring 53 second from the top end downwardly. The downward thrust is transmitted to the third track ring 53 through the intervening rigid spacing ring 56, through the balls 59 engaging the third track ring 53 to the uppermost double inner track ring 58, and through the next lower ring of balls 59 to the fourth outer track ring 53, the thrust being similarly transmitted through the remaining balls and track rings to the bottom of the stack. Thus the pressure between all the balls 59 and their cooperating track rings is increased.

The inner track rings are arranged between end plates 71 and 72 on the driving shaft 49, the plates 71 and 72 being shaped to guide the material into the first pass at the upper end of the machine and away from the driving shaft at the lower end of the machine.

in the machine shown in Figures 1 and 2, the air flowing through the machine has a cooling effect. Alternatively, or in addition, cooling may be effected by liquid flowing through an annular chamber 73, as shown in Figure 3.

It will be understood that any desired number of pairs of grinding stages in addition to the two stages associated with the driving means may be provided, three additional pairs being shown in Figure 3 merely by way of example.

I claim:

1. A grinding machine of the type referred to comprising a fixed track ring provided at its radially inner side with a track of arcuate cross section, a rotatable shaft extending through the fixed track ring a rotatable track ring on said shaft, a track on said rotatable track ring,

a set of grinding balls arranged between the fixed track ring and the rotatable track'ring, and driving means between the shaft and the rotatable track ring so arranged that the torque reaction during rotation of the shaft tends to urge the rotatable track ring axially along the shaft, the track on the rotatable trackring being so shaped that the axial thrust on the said ring urges the grinding balls outwardly against the fixed track ring.

2. A grinding machine according to claim 1, having two axially spaced fixed track rings, and two rotatable track rings on said shaft, two sets of grinding balls being provided, each between one fixed track ring and one rotatable track ring, the driving means being so arranged that the two rotatable track rings are urged axially in opposite directions.

3. A grinding machine according to claim 1, wherein the driving means comprises a screw mechanism.

4. A grinding machine according to claim 2, wherein at least two additional sets of grinding balls are provided, the outer track ring associated with one of said additional sets of balls being arranged for axial displacement by thrust applied thereto by the outer track ring associated with one of the sets of balls the inner race of which is acted on by the driving means, and the inner track rings associated with said additional sets of balls being axially movable and either integral or movable together as one.

5. A grinding machine according to claim 4, wherein a compressible spacing ring is interposed between the outer track rings associated with the two additional sets of grinding balls.

6. A grinding machine comprising a fixed track ring, a track of arcuate cross-section provided on the radially inner side of said fixed track ring, a rotatable shaft extending through said fixed track ring, a rotatable track ring, a track on said rotatable track ring, a set of grinding balls arranged between the fixed track ring and the rotatable track ring, a helical groove in the rotatable shaft, a helical groove in the rotatable track ring, and a plurality of driving balls engaging in both said helical grooves, whereby torque reaction during rotation of the shaft tends to urge the rotatable track ring axially along the shaft, the track on the rotatable track ring being so shaped that the axial thrust on the said ring urges the grinding balls outwardly against the fixed track ring.

7. A grinding machine comprising two axially spaced fixed track rings, a track of arcuate cross-section provided on the radially inner side of each said fixed track ring, a rotatable shaft extending through both of said fixed track rings, two rotatable track rings, a track on each rotatable track ring, two sets of grinding balls each arranged between one fixed track ring and one rotatable track ring, two helical grooves of mutually opposite hand in said rotatable shaft, a helical groove in each of said rotatable track rings each of said last-mentioned grooves being of the same hand as one groove in the rotatable shaft, and two sets of driving balls each engaging in a helical groove in the rotatable shaft and the helical groove of the same hand in a rotatable track ring, whereby torque reaction during rotation of the shaft tends to urge the rotatable track rings in opposite directions axially along the shaft, the tracks on the rotatable track rings being so shaped that the axial thrust on the said rings urges the grinding balls outwardly against the fixed track rings.

References Cited in the file of this patent UNITED STATES PATENTS 862,720 Day Aug. 6, 1907 1,499,624 Middleboe July 1, 1924 2,204,140 Langbein June 11, 1940 

